Circuit and photo sensor overlap for backside illumination image sensor

Abstract

A method of operation of a backside illuminated (BSI) pixel array includes acquiring an image signal with a first photosensitive region of a first pixel within the BSI pixel array. The image signal is generated in response to light incident upon a backside of the first pixel. The image signal acquired by the first photosensitive region is transferred to pixel circuitry of the first pixel disposed on a frontside of the first pixel opposite the backside. The pixel circuitry at least partially overlaps the first photosensitive region of the first pixel and extends over die real estate above a second photosensitive region of a second pixel adjacent to the first pixel such that the second pixel donates die real estate unused by the second pixel to the first pixel to accommodate larger pixel circuitry than would fit within the first pixel.

1. A method of operation of a backside illuminated (BSI) pixel array including at least a first pixel and a second pixel adjacent to the first pixel, the method comprising:
 acquiring an image signal with a first photosensitive region of the first pixel, the image signal generated in response to light incident upon a backside of the first pixel; and 
 transferring the image signal acquired by the first photosensitive region to pixel circuitry of the first pixel disposed on a frontside of the first pixel opposite the backside, wherein the pixel circuitry of the first pixel at least partially overlaps the first photosensitive region of the first pixel and extends over die real estate above a second photosensitive region of the second pixel such that the second pixel donates die real estate unused by the second pixel to the first pixel to accommodate larger pixel circuitry than would fit within the first pixel. 
 
     
     
       2. The method of  claim 1 , further comprising for the first pixel:
 resetting the first photosensitive region prior to acquiring the image signal by temporarily enabling a reset transistor coupled between a voltage rail and the first photosensitive region, wherein the reset transistor is disposed on the frontside of the first pixel and wherein the reset transistor at least partially overlaps the first photosensitive region. 
 
     
     
       3. The method of  claim 1 , further comprising for the first pixel:
 converting the image signal to a digital image signal with an analog-to-digital converter (“ADC”) disposed on the frontside of the first pixel, wherein the ADC at least partially overlaps the first photosensitive region. 
 
     
     
       4. The method of  claim 1 , further comprising for the first pixel:
 amplifying the image signal with gain circuitry disposed on the frontside of the first pixel, wherein the gain circuitry at least partially overlaps the first photosensitive region. 
 
     
     
       5. The method of  claim 2 , further comprising for the first pixel:
 performing image signal processing with additional circuitry disposed at least partially within the first pixel and which at least partially overlaps the first photosensitive region. 
 
     
     
       6. The method of  claim 1 , wherein the BSI pixel array comprises a complementary-metal-oxide-semiconductor (“CMOS”) pixel array. 
     
     
       7. The method of  claim 6 , wherein the first and second photosensitive regions comprises photodiodes. 
     
     
       8. The method of  claim 1 , wherein transferring the image signal acquired by the first photosensitive region comprises transferring an image charge through an interlinking diffusion region coupled between the first photosensitive region and the pixel circuitry disposed on the frontside. 
     
     
       9. The method of  claim 1 , further comprising:
 reading out the image signal of the first pixel via the pixel circuitry to output the image signal from the BSI pixel array.